DE102015201048A1 - Method for producing a carbon layer on an output structure and microelectromechanical or semiconductor structure - Google Patents

Abstract

The invention relates to a method for producing a microelectromechanical or a semiconductor structure, comprising the steps of providing an initial structure whose surface comprises at least portions consisting of silicon dioxide, providing a starting material or a mixture of a plurality of starting materials, which in a LPCVD process is a mixture from carbon, silicon and chlorine - introducing the starting structure and the one or the mixture of the starting materials in the LPCVD process and thus - depositing a carbon layer on the silicon dioxide existing portions of the starting structure and a microelectromechanical or semiconductor structure, which is produced by the method ,

Description

State of the art

Various methods are described in the literature for applying carbon layers on a MEMS (= micro-electro-mechanical sensor) or a semiconductor substrate.

It is known, for example, the detachment of a carbon layer from a graphite block or HOPG (Highly Oriented Pyrolytic Graphite) by means of an adhesive tape, transfer of the layer to the substrate and subsequent dissolution of the adhesive tape. With this method, only relatively randomly positioned and oriented carbon flocks can be produced on the substrate. In addition, it is a manual procedure, so it is not suitable for industrial and in particular large-scale application.

Also known is the decomposition of organic materials on a substrate. This creates all possible carbon configurations.

Also known is the deposition of carbon layers by means of epitaxial growth. The required metallic substrates are not provided in the field of semiconductor manufacturing.

Also known is the effect of a temperature-dependent solubility of the carbon in transition metals, which freezes the carbon at rapid lowering of the temperature. For this purpose, in turn, metals on the substrate are required.

Also known is the evaporation of silicon from a silicon carbide crystal with a suitable crystal orientation at the surface. Due to the absence of silicon, the carbon orients itself in a desired configuration. For this purpose, high temperatures and very expensive silicon carbide substrate are needed.

Furthermore, it is known that in an LPCVD process using a pure silicon precursor and a sufficient amount of chlorine, no silicon deposition takes place on a substrate coated with SiO.sub.2 (see, for example, US Pat J. Electrochem. Soc. 1986 volume 133, issue 2, 379-383 ).

Advantages of the invention

The present invention describes a deposition process in the LPCVD process for carbon films, which is suitable for a MEMS (= micro-electro-mechanical sensor) process or a semiconductor process. The particular carbon configuration produced thereby makes this invention interesting for novel applications in the nanoscale. LPCVD (Low Pressure Chemical Vapor Deposition) refers to a chemical process for the production of layers on substrates in the context of the production of micromechanical sensors or semiconductor structures.

The LPCVD process according to the invention makes it possible to deposit thin carbon layers on a layer of silicon dioxide (SiO ₂ ). The main idea of this LPCVD process is that in addition to the carbon precursor chlorine and silicon is used. As a result, in the selected process parameters on the SiO ₂ , despite the silicon content in the process gas atmosphere, no silicon and also silicon-carbon compound are deposited, but rather a pure carbon layer. In contrast to many processes for the deposition of carbon layers, such as diamond like carbon (DLC = English: Diamond Like Carbon), this process is not a plasma-assisted process, but a purely thermally activated process, which advantageously the deposition In addition, it is not necessary to use metal catalysts for the decomposition of carbon precursors, as is the case for known carbon deposition processes.

The invention is suitable for applying carbon layers on a MEMS (= micro-electro-mechanical sensor) or a semiconductor substrate. The invention is also particularly suitable for, in particular automated, mass production with high reliability and process reliability and allows low reject rates.

The invention advantageously enables a planar and targeted deposition of a carbon layer on defined and selectable positions of a semiconductor material wafer. No starting layers which are unusual or unsuitable for the semiconductor industry are required, silicon dioxide (SiO ₂ ) can serve as a starting layer for the carbon layer. There are no metals needed. The carbon layer can be mechanically and electrically contacted in situ. It is an LPCVD process that requires no special system modifications and can be carried out with established process gases.

The carbon layers produced by the process according to the invention have well-known, advantageous properties. These are u.a. a high electrical conductivity, high mobility of the charge carriers and a high mechanical strength of the few nanometers thick carbon layer.

An advantageous property consists in a high electrical conductivity of the carbon layer combined with a high mobility of the charge carriers. Thus, the layers are suitable, for example, for the production of THz transistors, capacitors with high energy density and for storing large amounts of energy, so-called supercaps and batteries, the further Hall effect-based magnetic sensors and transparent interconnects or electrodes, for example for displays.

The carbon layers produced also allow chemical functionalization, such as for use in or in gas sensors or medical technology.

The carbon layers produced also have a high mechanical strength at low density with additional piezoresistive or piezoelectric properties and thus are suitable for example for use in spring structures for resonators such. Micromirrors or inertial sensors.

• – Bereitstellen einer Ausgangsstruktur, deren Oberfläche zumindest Abschnitte bestehend aus Siliziumdioxid aufweist,
• – Bereitstellen eines Ausgangsstoffes oder einer Mischung mehrerer Ausgangsstoffe, welche in einem LPCVD-Prozess eine Mischung aus Kohlenstoff, Silizium und Chlor abgeben
• – Einbringen der Ausgangsstruktur und des einen oder der Mischung der Ausgangsstoffe in den LPCVD-Prozess und damit
• – Abscheiden einer Kohlenstoffschicht auf den aus Siliziumdioxid bestehenden Abschnitten der Ausgangsstruktur.

The method according to the invention comprises the steps

• Providing an initial structure whose surface comprises at least portions consisting of silicon dioxide,
• - Providing a starting material or a mixture of multiple starting materials, which emit in a LPCVD process, a mixture of carbon, silicon and chlorine
• - Introducing the starting structure and the one or mixture of starting materials in the LPCVD process and thus
• Depositing a carbon layer on the portions of the starting structure made of silicon dioxide.

Advantageously, the LPCVD process is carried out under certain favorable process conditions, namely at a process temperature in a range between 700 ° C and 1300 ° C and at a process pressure in a range between 100 mTorr and 5000 mTorr. A suitable combination of parameters is, for example, a process temperature of 1020 ° C with a process pressure of 875 mTorr. There is a particularly high reliability of the process with the lowest possible reject rate.

According to an advantageous embodiment of the invention, the starting structure, in addition to the sections consisting of silicon dioxide, may have further sections, which may be e.g. made of silicon (Si) and / or silicon carbide (SiC). This ensures that a silicon carbide layer is deposited on these further sections in the LPCVD process. This advantageously forms a mechanical and electrical connection with the deposited carbon layer and can thus support or support it.

This is of particular interest and importance if, according to a further development of the invention, the portions of the starting structure consisting of silicon dioxide below the carbon layer are completely or partially removed, preferably by means of gas phase etching, after completion of the LPCVD process. Hydrofluoric acid can be advantageously used for gas phase etching.

In order to provide the substances required for the deposition of a carbon layer according to the invention in the LPCVD process, methyltrichlorosilane can be advantageously used as starting material. Alternatively, for example, a mixture of silane, methane and hydrogen chloride can be used. Furthermore, other starting materials can be used which represent comparable sources of carbon, silicon and chlorine under the process conditions of the LPCVD process. In addition, other gases, e.g. Hydrogen as a carrier gas or ammonia as a source for doping the SiC layer.

Furthermore, the invention is directed to a micromechanical structure or a semiconductor structure which has been produced by the method according to the invention.

drawings

Embodiments of the invention are illustrated in the figures and are explained in more detail below. Show it

1 a schematic representation of a section through the layer structure of an inventively produced MEMS or semiconductor structure, which represents the initial structure for the selective carbon deposition.

2 2 a schematic representation of a section through the layer structure of a MEMS or semiconductor structure produced according to the invention as an example of the variant in which silicon carbide (SiC) support structures were also produced in addition to the carbon layer,

3 a schematic representation of the structure according to 2 in contrast to 2 the SiO 2 layer has been removed under the carbon layer,

4 a schematic representation of a section through a semiconductor structure produced by the method according to the invention using the example of a transistor.

Description of the embodiments

The present invention utilizes an LPCVD process to deposit thin carbon layers, which are, for example but not necessarily, crystalline and are on a layer of SiO 2. Essential in the deposition of this layer is that no pure carbon precursor (carbon precursor) is used, but a starting material or a starting material mixture is used, the or in addition to carbon and typically also hydrogen, the process also chlorine and silicon available , This can be achieved by using a single precursor, such as methyltrichlorosilane. It is also conceivable to use about three different precursors, each of which represents a source of carbon, silicon and chlorine, such as silane, methane and hydrogen chloride. It is essential that starting materials are used which, under the process conditions of the LPCVD process, are sources for the required elements of carbon, chlorine and silicon concentration.

With, for example, the abovementioned gas combination silane, methane and hydrogen chloride, thin layers of silicon carbide (SiC) can be deposited on a simple silicon substrate in the LPCVD process. However, if a layer of SiO.sub.2 is present on the substrate, no SiC layer grows thereon under suitable process conditions, but a thin, pure carbon layer which, in the case of suitably selected process parameters, develops in a desired carbon configuration. For this selective process, it is crucial that a SiO2 layer is present and sufficient chlorine is present in the process.

For this purpose, it is hitherto known that when using a pure silicon precursor and a sufficient amount of chlorine no silicon deposition takes place on a SiO 2 substrate (see, for example, US Pat J. Electrochem. Soc. 1986 volume 133, issue 2, 379-383 ).

With the simultaneous addition of carbon, in the form of a precursor, e.g. Methytricholorsilan (MTS), no further silicon compound on the SiO 2 layer is deposited, but a carbon layer. To achieve this selective process, moderate to high process temperatures (700-1300 ° C) and low process pressures (100-5000 mTorr) are required.

The selectivity of the process over SiO 2 can also be used to advantage in that it is based on a starting layer of e.g. Si, SiC, another layer of SiO 2 is applied and this SiO 2 layer is then patterned. In the following LPCVD process, an SiC layer grows in the areas without SiO 2, whereas in the areas with SiO 2 the carbon layer grows. This carbon layer is considerably thinner than the SiC layer. In addition, a mechanical and an electrical contact between the SiC and the carbon layer arises.

In 1 is schematic and exemplary an initial structure 1 represented, which is to be processed by the method according to the invention. The initial structure 1 has a substrate 10 from, for example, silicon, over which a so-called start layer 11 , For example, consisting of silicon (Si) or silicon carbide (SiC) is arranged. Section or section wise is the start layer 11 covered with a layer of silicon oxide (SiO 2). At the initial structure of 1 are four areas or sections 12-1 . 12-2 . 12-3 . 12-4 (summarized below) 12-x ) consisting of silicon oxide on the starting layer 11 arranged, being between the areas 12-x Void spaces exist, so that in these void spaces the surface of the initial structure 1 through the exposed portions of the starting layer 11 is formed. The surface of the starting structure is thus replaced by a sectionally or partially SiO 2 layer and regions or sections of the exposed starting layer lying therebetween or adjacent to it 11 educated.

This provided (step 31 in 5 ) Initial structure 1 is introduced into the process room of an LPCVD plant in which the subsequent LPCVD process is carried out. For the LPCVD process, the appropriate process parameters, such as, in particular, the process pressure and process temperature are set in the above range, as well as the aforementioned provided (step 32 ) Supplied process chemicals (step 33 ). Examples of suitable process parameters are pressure p = 874 mTorr, temperature T = 1020 ° C with the addition of the gases hydrogen (flow 425 sccm) and MTS (flow 35sccm). As a result of the deposition (step 34 ) is a semiconductor or MEMS structure (hereinafter referred to simply as a semiconductor structure) according to 2 in front.

The semiconductor structure generated by the described LPCVD process 1' again comprises the substrate 10 , about the start layer 11 as well as sections of the above-stored areas 12-x made of silicon oxide. As a result of the LPCVD process are on the between the SiO2 sections 12-x lying directly behind the LPCVD process exposed areas of the starting layer silicon carbide sections 13-1 . 13-2 and 13-3 grew up. On the other hand, on the SiO2 sections 12-x one layer each 14-1 . 14-2 . 14-3 and 14-4 (summarized below) 14-x ) deposited from carbon. The silicon carbide layer and the carbon layer have very different thicknesses depending on the time of deposition. While the carbon layers are only a few atomic layers a few nm thick (<20 nm, with process times of 60 min), the silicon carbide layers of the same process are several hundred nm thick. The specific resistance of the silicon carbide layer is dependent on the doping, by an addition of ammonia, but no values less than 10mOhmcm are achieved. On the other hand, the carbon layer may have a resistivity of 1mOhmcm, with a high degree of crystallinity.

As a consequence of the described LPCVD process, the carbon layers are 14-x with the respective adjacent silicon carbide sections 13-x mechanically and electrically connected. As a result of the mechanical connection, the silicon carbide layers or sections 13-1 . 13-2 . 13-3 as supports for the adjacent carbon layers 14-x serve, for example, in a subsequent processing step 35 backed off, that is, the SiO2 sections carrying them 12-x be removed by etching, for example, gas phase etching with hydrofluoric acid. This creates a structure 1'' as in 3 shown in which the carbon layer sections 14-x about empty spaces 15-1 . 15-2 . 15-3 and 15-4 from the respective adjacent SiO2 sections 12-x be worn and held.

For selective carbon deposition 14-x is the existence of a SiO2 surface 13-x essential, wherein the layer thickness is insignificant. This can be advantageously used, for example, to use extremely thin SiO 2 layers, for example in function as gate oxides.

This process can be used to advantage in order to transistors 2 build up with carbon layer, as in 5 sketched, taking on the last step 35 is omitted to obtain the gate oxide. On a substrate 20 , For example, silicon, is an electrically insulating layer 21 applied thereto, such as silicon oxide (SiO 2), thereupon becomes an electrically conductive layer 22-1 . 22-2 . 22-3 applied, which may for example consist of poly-silicon or silicon carbide. The thickness of the layer can be selected as needed and be a few nanometers (nm) to a few micrometers (μm). This layer 22-x is structured such that electrical wiring and the contacts for drain 23-1 , Source 23-2 and in the gate area 22-2 arise. Subsequently, a thin SiO2 layer 25 over the gate 22-2 applied. The subsequent selective structuring according to the invention makes it possible for a carbon layer to be formed 24 on the gate oxide 25 which forms the channel of the transistor 2 On the other hand, the carbon layer is deposited over the depositing SiC 23-1 and 23-2 electrically contacted to drain and source. In contrast to the normal transistors, the channel lies on the surface and not the gate electrode. For sensors in this configuration, in addition to the channel-gate potential, additional effects can be sensed that affect the conductivity in the channel 24 influence.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• J. Electrochem. Soc. 1986 volume 133, issue 2, 379-383 [0007]
• J. Electrochem. Soc. 1986 volume 133, issue 2, 379-383 [0029]

Claims (9)

Method for producing a microelectromechanical or a semiconductor structure, comprising the steps - providing ( 31 ) an initial structure ( 1 ) whose surface has at least sections ( 12-1 . 12-2 . 12-3 . 12-4 ) consisting of silicon dioxide, - providing ( 32 ) of a starting material or a mixture of several starting materials, which release a mixture of carbon, silicon and chlorine in an LPCVD process - introduction ( 33 ) of the initial structure ( 1 ) and the one or the mixture of the starting materials in the LPCVD process and thus - deposition ( 34 ) a carbon layer ( 14-1 . 14-2 . 14-3 . 14-4 ) on the sections of silicon dioxide ( 12-1 . 12-2 . 12-3 . 12-4 ) of the initial structure ( 1 ). A method according to claim, characterized in that the LPCVD process is carried out at a process temperature in a range between 700 ° C and 1300 ° C and at a process pressure in a range between 100 mTorr and 5000 mTorr. Method according to claim 1 or 2, wherein the starting structure ( 1 ) next to the silicon dioxide sections ( 12-1 . 12-2 . 12-3 . 12-4 ) has further sections, which consist of silicon and / or silicon carbide, and thus - deposition of a silicon carbide layer ( 13-1 . 13-2 . 13-3 ) on the silicon or silicon carbide other sections of the starting structure ( 1 ) in the LPCVD process. Procedure ( 35 ) according to one of the preceding claims, in particular according to claim 3, characterized in that the sections consisting of silicon dioxide ( 12-1 , ..., 12-4 ) of the initial structure ( 1 ) below the carbon layer ( 14-1 , ..., 14-3 ) after completion of the LPCVD process, in whole or in part, preferably by means of gas phase etching removed. A method according to claim 4, characterized in that for gas phase etching hydrofluoric acid is used. Method according to one of the preceding claims, characterized in that methyltrichlorosilane is used as starting material. Method according to one of claims 1 to 5, characterized in that as starting material a mixture of silane, methane and hydrogen chloride or under the process conditions of the LPCVD process comparable sources for carbon, silicon and chlorine performing substances are used. The method of claim 3, wherein additionally a nitrogen source, such as ammonia, is used to achieve doping of the deposited silicon carbide layer Microelectromechanical or semiconductor structure ( 1 . 2 ) prepared by a method according to any one of the preceding claims.

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